Diel Vertical Migration

Why Did Vertical Migration Evolve? 1. Seek Optimal light intensity but why?? 2. Avoid visual predators 3. Utilization of different water masses (Hardy 1956) 4. Energy conservation (McLaren 1963) 5. Optimization of food (Enright 1977) 6. Ladder of migration (larger plankton and nekton)

Nutrients PP ZPFish Bottom up Top down Heterogeneity basis

Density-dependent feeding

Assimilation efficiency % assimilated = ingested – waste ingested pp concentration  % assimilated

Is zooplankton mortality food-dependent?

Lag time and positive feedback loops

Nutrients PP ZPFish Critical factors affecting phytoplankton production-PS, growth rates, maintenance of biomass Bottom up - nutrient and light limits Top down – predation, competitoin

Ocean ecosystem – classic model - PS – phytoplankton production- copepods – predators – detritus PS – phytoplankton production- copepods – predators – detritus Pacific – tightly coupled – copepods graze most of plankton, production and energy in pelagic fish Pacific – tightly coupled – copepods graze most of plankton, production and energy in pelagic fish Atlantic, loosely coupled, production and energy in benthic fish via debris Atlantic, loosely coupled, production and energy in benthic fish via debris

Ultra and Nanoplankton < 30 microns, Bacterioplankton, flagellates, cocoliths Diatoms, dinoflagellate driven model still holds for upwelling, coastal waters. Why is this recent? Can account for 75% biomass, 80% production in epipelagic oceanic zone Production & population size not seasonally variable. Esp tropics, gyres – why there ? Advantage to small size? Advantage to small size? Low nutrients & >s/v, s/v, < needs, protist symbionts in larger planktonic protozoa

Bacterioplankton DOC huge reservoir, stable DOC huge reservoir, stable But ~ ¼ of PS fixed C is “leaked” as DOM - ??cont. production of C vs stable amt? Where does it go? Why not build up? But ~ ¼ of PS fixed C is “leaked” as DOM - ??cont. production of C vs stable amt? Where does it go? Why not build up? Up to 50% of total ocean production via direct bacterial uptake ( DOM + particles living and dead) Up to 50% of total ocean production via direct bacterial uptake ( DOM + particles living and dead) Bacterioplankton ext. abundant ~ 0.4 micron Bacterioplankton ext. abundant ~ 0.4 micron “lost” production really recycled via bacteria into food chain “lost” production really recycled via bacteria into food chain refractory DOM – humic acids, lignins refractory DOM – humic acids, lignins Dynamic DOM – amino acids, sugars, vitamins Dynamic DOM – amino acids, sugars, vitamins –High turnover; used by auxotrophs, heterotrophs

Nano food web –Macro phyto production – DOM by leakage and lysis, plus photosynthesis, drives nano loop – regenerates/creates nutrients –Bacterioplankton < 1 micron = 90% DOM uptake, 60-65% assimilation efficiency –High efficiency = convert DOM into POC –Nano biomass>> macro phyto plankton –Predators - ciliates, non-photo flagellates –Consume most nanoplankton production, consumed by macro plankton

Sources of DOM 1. PP cells are inherently “leaky - normal, healthy cells exude 1-20% of fixed carbon - senescent cells even more leaky 2. Autolysis +/or bursting of old, injured, virus- infected cells 3. Exudates to serve functional need of cell - auxotrophs to attract vitamin-producers - competitive interference - water conditioners

Sources of DOM 4. Loss during ingestion - zp sloppy eaters, especially high grazing rate areas 5. Excretion - about 10% of C ingested Bacteria regenerate nutrients in low nutrient waters

DOM Utilization Direct – primarily bacteria, but some zooplankton Direct – primarily bacteria, but some zooplankton Indirect – extra links in ignored food chain Indirect – extra links in ignored food chain “microbial loop”

Marine snow – organic aggregates Air bubbles breaking Air bubbles breaking Adsorption to silt particles, salt crystals Adsorption to silt particles, salt crystals Cast off molt skins, mucus nets, fecal pellets, etc. Cast off molt skins, mucus nets, fecal pellets, etc. Intense sites of bacterial decomposition, nutrient recycling

Paradox of the Plankton – T e = time between environmental changes T c = time to competitive exclusion T c T e T c ~ T e how can so many species coexist in a seemingly homogeneous ocean?

Are the Oceans Homogeneous?

Small-scale patchiness –Marine snow –Microturbulence –Vertical differences in light, other factors Moderate-scale patchiness –Coastal fronts –Langmuir circulation –Ocean eddies or rings

Large-scale patchiness –Major continental upwelling zones –Equatorial upwelling zones –Current convergence zone –Major ocean gyre systems

Biological Interactions (top down) –Grazing –Variations in reproductive rate –Social behavior –Interspecific interactions that attract or repulse